This invention relates generally to devices for metering the flow of refrigerant in a vapor compression refrigeration system. More particularly, the invention relates to a metering device that is effective in reducing refrigerant flow noise during both steady state operation and after shutdown of the refrigeration system in which the device is installed.
One of the essential components of a closed cycle vapor compression refrigeration system is a metering or expansion means for effecting a drop in the refrigerant pressure at one point in the cycle, thus causing a change of refrigerant state from liquid to gas and a reduction in refrigerant pressure and temperature due to adiabatic expansion. Many types of such metering devices are known in the art, including thermoexpansion valves, Accurator.RTM., orifices and capillary tubes. Capillary tubes, because of their relatively small size and low cost, are commonly found in small to medium capacity refrigeration systems such as room air conditioners and packaged terminal air conditioners.
An objective in the design and manufacture of a refrigeration system, particularly one that is intended to operate in or near inhabited areas, is to reduce the sound radiated by the system, not only during operation but also during post shutdown transients. One source of sound in a refrigeration system is the metering device. High velocity liquid refrigerant passing through a capillary tube metering device during system operation can be a source of objectionable noise. The passage of high velocity gaseous refrigerant through a capillary tube metering device during system shutdown can also radiate noise of a different but still objectionable nature.
What is needed therefore, is a metering device that reduces the radiated noise level of a vapor compression refrigeration system.